The current regimen for treating tuberculosis (TB) involves multiple antibiotics, is long and arduous and has contributed to the emergence of drug-resistant TB. Improving anti-TB chemotherapy by shortening treatment and enhancing efficacy is therefore a high priority for global TB control. Manipulating the host immune response to reduce the harmful effects of Mtb-induced immune responses may enhance the efficacy of antibiotics. We hypothesize that blocking the functions of a key Mycobacterium tuberculosis (Mtb) immunomodulatory protease, Hip1, will create a more favorable in vivo immune milieu for resolving infection, leading to accelerated clearance of Mtb by antibiotics and shortened treatment. This concept of targeting pathogen-specific virulence factors to improve treatment outcomes has not previously been explored. Studies from our group have shown that Hip1 promotes detrimental innate and adaptive immune responses in Mtb- infected macrophages, dendritic cells and mice. Absence of Hip1 is beneficial to the host as this results in mild immunopathology and prolonged survival of infected mice despite high bacterial burdens in vivo. Thus we propose that inhibiting Hip1 is attractive for developing adjunctive immune therapeutics for TB. We will use the C3HeB/FeJ mouse model of TB chemotherapy to test the hypothesis that silencing hip1 in conjunction with anti-TB treatment will reduce pathology and tissue damage in the lung and accelerate clearance of Mtb. We propose the following proof of concept studies: Aim 1. Determine whether silencing hip1 improves clearance of Mtb during anti-TB chemotherapy in a mouse model of TB. We will infect mice with a conditional hip1 knockdown strain and assess bacterial clearance at time points following antibiotic treatment, and evaluate the occurrence of relapse compared to controls. Aim 2. Characterize the effect of hip1 silencing on lung immune responses and granulomatous pathology during chemotherapy. We will compare inflammatory responses, antigen-specific T cell responses and the nature of lung granuloma lesions induced by infection with wild type and hip1 knockdown Mtb strains before, during and after treatment. These studies will give us important insights into whether inhibition of Hip1 is a feasible approach for adjunctive immune therapy and provide a framework for testing candidate Hip1 inhibitors in vivo.